We have developed a hybrid molecular/MOSFET, which is sensitive to the presence of a molecular layer attached to its surface. The application of the molecular layer was investigated by observing changes in the drain current as a function of substrate voltage pre-and post molecular treatment. A significant shift in the threshold current of the device was observed after application of the molecules. The threshold shift can be attributed to an increase in the electron charge density in the MOSFET channel, resulting from an increase in the positive fixed charge at the native oxide surface. A numerical simulation supports this conclusion. It is speculated that the molecules protonate the surface of the SiO 2 due to the higher acidity of the molecular groups compared to that of the native oxide. To assess the validity of this hypothesis a series of molecules with similar structure but with different acidities (pKa values) were investigated, to correlate the shift in threshold voltage with the difference in pKa value between the applied chemical and the SiO 2 surface (pKa ΒΌ 6.8). Preliminary results showing the systematic variation of DV th and pKa are presented.